The player who Swisher essentially replaced, Bobby Abreu, was the better player for most of this year (in terms of RAR (Runs Above Replacement)), but recently, primarily due to defense, Swisher has taken the lead in the 'Who would the Yankees rather have in rightfield?' contest.
So despite Abreu having a slightly better offensive year (17.8 vs. 16.4 RAR), the large difference in defense (12 runs) makes Swisher the better player. He's accounted for 29 Runs Above Replacement while Abreu, just 21.
Even in the pitch taking department, Swisher is better. He sees 4.27 pitches/PA while Abreu sees (a still impressive) 4.15. Swisher is eighth in MLB (second in the AL) in pitches/PA. Abreu is 25th (10th in the AL).
Outside of all the stats, I personally enjoy watching Swisher more than Abreu. He always has a smile on his face, has fun on the field, isn't afraid of the rightfield wall (as evidenced by his fine play last night), and last but not least, has a freakin' mohawk. Do any of these make the team better? Who really knows. I'm not a believer in 'chemistry' having an impact on winning, but from a fan's perspective, I love having him on my team.